A New Approach to Solution‐Phase Gold Seeding for SERS Substrates

Surface-enhanced Raman scattering (SERS) vastly improves signal-to-noise ratios compared to traditional Raman scattering, making sensitive assays based upon Raman scattering a reality. However, to date, preparation of highly stable SERS-active gold substrates requires complicated and expensive methodologies and instrumentation. Here, we introduce a general and completely solution phase, seed-based approach, capable of producing gold films for surface-enhanced Raman scattering (SERS) applications on a variety of substrates, not requiring surface modification or functionalization. SERS enhancement factors of ∼107 were observed. Moreover, solution-phase gold film deposition on highly complex surfaces, such as protein-coated bioassays, is demonstrated for the first time. Protein bioassays coated with such SERS-active gold films were combined with bioconjugated single-walled carbon nanotube Raman labels, affording high sensitivity detection of the cancer biomarker, carcinoembryonic antigen in serum, with a limit of detection of ∼5 fM (1 pg / mL).